Pulse Stretching Technique for Laser Bond Inspection, Laser Ultrasonic Inspection, and Laser Peening

ABSTRACT

An example laser system includes a laser, a plurality of pulse stretchers coupled together in series, a feedback module, and a lens assembly. The plurality of pulse stretchers is configured to stretch pulse widths of laser pulses provided by the laser and to output stretched laser pulses. The feedback module includes a pulse delay comparator that is configured to compare a first laser pulse of the laser pulses to a corresponding first stretched laser pulse of the stretched laser pulses. The feedback module also includes a computing device that is configured to determine, based on a result of the comparing by the pulse delay comparator, an adjustment to a pulse stretcher of the plurality of pulse stretchers, and apply the adjustment to the pulse stretcher so as to modify a shape of a second stretched laser pulse of the stretched laser pulses.

FIELD

The present disclosure relates generally to non-destructive testing, andmore particularly, to systems and methods for non-destructive testingusing lasers.

BACKGROUND

Various non-destructive testing systems use lasers. By way of example,laser bond inspection systems use lasers to evaluate the bond strengthof adhesive bonds in composite structures. To evaluate the bond strengthof an adhesive bond within a composite structure, an absorbing overlayand a transparent overlay can be provided on the composite structure.The laser bond inspection system can then cause a laser to emit a pulsethat passes through the transparent overlay and is absorbed by theabsorbing overlay. The absorption by the absorbing layer exerts pressureon the composite structure, thereby driving a stress wave into thecomposite structure. The laser bond inspection system can control thestrength of the pulse such that the stress wave will cause the adhesivebond to fail if the bond is weak, but will have no effect on theadhesive bond if the adhesive bond is sufficiently strong. If the stresswave causes the adhesive bond to fail, the failure can be detected by asensor positioned on the surface of the composite structure.

Laser ultrasonic inspection systems also use lasers. More specifically,laser ultrasonic inspection systems use lasers to detect defects, suchas delaminations, inclusions, voids, or disbonds, in structures. Forexample, a laser ultrasonic inspection system can cause a laser to emitpulses that contact a surface of a structure, thereby generatingultrasonic waves. The ultrasonic waves can then interact with featureson an interior of the structure, and propagate to the surface of thestructure. A detector of the laser ultrasonic inspection system can thenmeasure the ultrasonic waves, and the laser ultrasonic inspection systemcan analyze the measured ultrasonic waves to determine one or morecharacteristics of the structure.

SUMMARY

In one example, a laser system is described. The laser system includes alaser, a plurality of pulse stretchers coupled together in series, afeedback module, and a lens assembly. The laser is configured to providelaser pulses. The plurality of pulse stretchers is configured to stretchpulse widths of the laser pulses and output stretched laser pulses. Thefeedback module includes a pulse delay comparator and a computingdevice. The pulse delay comparator is configured to compare a firstlaser pulse of the laser pulses to a corresponding first stretched laserpulse of the stretched laser pulses. The computing device is configuredto (i) determine, based on a result of the comparing by the pulse delaycomparator, an adjustment to a pulse stretcher of the plurality of pulsestretchers, and (ii) apply the adjustment to the pulse stretcher so asto modify a shape of a second stretched laser pulse of the stretchedlaser pulses. The lens assembly is configured to output the secondstretched laser pulse.

In another example, an inspection system is described. The inspectionsystem includes a laser system and a detector. The laser system includesa laser, a plurality of pulse stretchers coupled together in series, afeedback module, and a lens assembly. The laser is configured to providelaser pulses. The plurality of pulse stretchers is configured to stretchpulse widths of the laser pulses and output stretched laser pulses. Thefeedback module is configured to adjust a parameter of at least onepulse stretcher of the plurality of pulse stretchers based on acomparison of a first laser pulse of the laser pulses and acorresponding first stretched laser pulse of the stretched laser pulses.The lens assembly is configured to direct a second stretched laser pulseof the stretched laser pulses to a workpiece after the feedback moduleadjusts the parameter of the at least one pulse stretcher. The detectoris configured to detect a response of the workpiece to the secondstretched laser pulse.

In another example, a method for inspecting a workpiece bondline isdescribed. The method includes stretching a pulse width of a first laserpulse using a plurality of pulse stretchers coupled in series so as toobtain a first stretched laser pulse. The method also includes comparingthe first laser pulse and the first stretched laser pulse. In addition,the method includes adjusting a parameter of at least one pulsestretcher of the plurality of pulse stretchers based on a result of thecomparing of the first laser pulse and the first stretched laser pulse.Further, the method includes, after adjusting the parameter, stretchinga pulse width of a second laser pulse using the plurality of pulsestretchers so as to obtain a second stretched laser pulse. Stillfurther, the method includes delivering the second stretched laser pulseto the workpiece bondline. Still further, the method includes detectinga response of the workpiece bondline to the second stretched laserpulse.

The features, functions, and advantages that have been discussed can beachieved independently in various examples or may be combined in yetother examples further details of which can be seen with reference tothe following description and figures.

BRIEF DESCRIPTION OF THE FIGURES

The novel features believed characteristic of the illustrative examplesare set forth in the appended claims. The illustrative examples,however, as well as a preferred mode of use, further objectives anddescriptions thereof, will best be understood by reference to thefollowing detailed description of an illustrative example of the presentdisclosure when read in conjunction with the accompanying figures,wherein:

FIG. 1 illustrates an inspection system, according to an example.

FIG. 2 is a conceptual illustration of a laser system, according to anexample.

FIG. 3 illustrates a pulse stretcher, according to an example.

FIG. 4 illustrates a feedback module, according to an example.

FIG. 5 illustrates an ultrasonic inspection system, according to anexample.

FIG. 6 illustrates a laser bond inspection system, according to anexample.

FIG. 7 shows a flowchart of a method, according to an example.

FIG. 8 shows an additional operation for use with the method shown inFIG. 7.

FIG. 9 shows a flowchart of another method, according to an example.

DETAILED DESCRIPTION

Disclosed examples will now be described more fully hereinafter withreference to the accompanying figures, in which some, but not all of thedisclosed examples are shown. Indeed, several different examples may beprovided and should not be construed as limited to the examples setforth herein. Rather, these examples are provided so that thisdisclosure will be thorough and complete and will fully convey the scopeof the disclosure to those skilled in the art.

Described herein are laser systems as well as systems and methods forusing laser systems to inspect a structure or perform other tasks. Anexample laser system includes a laser configured to provide laserpulses, and a plurality of pulse stretchers coupled together in series.The plurality of pulse stretchers is configured to stretch pulse widthsof the laser pulses and output stretched laser pulses. For instance, afirst pulse stretcher of the plurality of pulse stretchers can receive alaser pulse output by the laser, and output a stretched laser pulse thathas a longer pulse width then the received laser pulse. A second pulsestretcher of the plurality of pulse stretchers can then receive andfurther stretch the stretched laser pulse. This process can be repeatedby each additional pulse stretcher in the plurality of pulse stretchers,until a final pulse stretcher of the plurality of pulse stretchersoutputs a stretched laser pulse. The stretched laser pulse output by theplurality of pulse stretchers can then be directed toward a surface of astructure by way of a lens assembly.

The laser system can also include a feedback module configured tocontrol a shape of the stretched laser pulse output by the plurality ofpulse stretchers. The feedback module can include a pulse delaycomparator and a computing device. The pulse delay comparator can beconfigured to compare a first laser pulse of the laser pulses to acorresponding first stretched laser pulse that has been stretched by theplurality of pulse stretchers. The computing device can also beconfigured to determine, based on a result of the comparing by the pulsedelay comparator, an adjustment to a pulse stretcher of the plurality ofpulse stretchers, and apply the adjustment to the pulse stretcher.

For instance, the pulse delay comparator can be configured to compare atrailing edge of the first laser pulse and a trailing edge of the firststretched laser pulse, and the adjustment could include an adjustment toa time delay introduced by the pulse stretcher. For instance, if thetrailing edge of the first laser pulse and the trailing edge of thefirst stretched laser pulse are separated in time by more than athreshold difference, the adjustment could be an increase to the timedelay introduced by the pulse stretcher. After adjusting the pulsestretcher, the laser can output a subsequent laser pulse and theplurality of pulse stretchers can output a subsequent stretched laserpulse, with the shape of the subsequent stretched laser pulse beingdifferent from the shape of the first stretched laser pulse.

Furthermore, the computing device can iteratively compare unstretchedand stretched laser pulses and make adjustments to pulse stretchers inorder to achieve an objective pulse shape. For instance, the computingdevice can make adjustments to respective time delays introduced by thepulse stretchers until the stretched laser pulse is uniform,square-shaped, and/or has a desired pulse width.

The laser systems disclosed herein can generate laser pulses having thedesired characteristics for laser bond inspection: pulse widths on theorder of 100 nanoseconds and pulse energies of 5 to 15 Joules.Conventional laser bond inspection systems generate laser pulses havingthese characteristics by routing a laser beam all over a large machine(e.g., a machine that is the size of a small truck) and through acomplex system of optical cavities and amplifiers. As a result, the sizeand cost of laser bond inspection systems is prohibitive for widespreadapplication of laser bond inspection. By using the laser systemsdisclosed herein as the laser source for a laser bond inspection system,less complex, smaller, and more cost-effective laser bond inspectionsystems can be made, thereby facilitating wider use of laser bondinspection technology. The presence of the pulse stretchers allows thesystem to operate with a laser that provides laser pulses withrelatively short pulse widths (e.g., a few nanoseconds, ten nanoseconds,twenty nanoseconds, etc.). Such a laser can have a smaller size and bemade more cost-effectively than lasers that provide pulses with longerpulse widths.

The laser systems disclosed herein can also be used in other systems.For instance, the laser systems disclosed herein can be used in laserultrasonic inspection systems and laser peening systems.

Various other features of these systems and methods are describedhereinafter with reference to the accompanying figures.

Referring now to FIG. 1, FIG. 1 illustrates an inspection system 100,according to an example. As shown in FIG. 1, inspection system 100includes a laser system 102, a detector 104, a positioning system 106,and an end effector 108. Laser system 102 and/or detector 104 can becoupled to or positioned within end effector 108. Laser system 102 anddetector 104 can also be in wired or wireless communication with eachother by way of one or more communication links or in wired or wirelesscommunication with a central computing device. Laser system 102,detector 104, positioning system 106, and end effector 108 can becomponents of a common apparatus. The apparatus may be a portableapparatus.

Laser system 102 can be configured to output laser pulses to a workpiece110. Workpiece 110 can include a composite structure that is joinedusing adhesive bonds. One example of a workpiece is an aerospacecomposite structure such as an aircraft wing or an aircraft body.

In line with the discussion above, laser system 102 can include variouscomponents that can be configured for controlling characteristics of thelaser pulses, such as the pulse energy and pulse repetition rate of thelaser pulses. More specifically, laser system 102 includes a laser 202,a plurality of pulse stretchers 204, a feedback module 206, and a lensassembly 208. Laser 202, plurality of pulse stretchers 204, feedbackmodule 206, and lens assembly 208 can be positioned proximate to eachother. For instance, laser 202, plurality of pulse stretchers 204,feedback module 206, and lens assembly 208 can be rigidly mounted to abase such that laser pulses can travel from laser 202 to plurality ofpulse stretchers 204, feedback module 206, and lens assembly 208.

Laser 202 is configured to provide laser pulses. For instance, laser 202can be an excimer laser or a neodymium glass laser. The pulse width ofthe laser pulses can vary from a few nanoseconds to as large as 30nanoseconds, depending on the desired configuration. Similarly, thepulse energy of the laser pulses can range from tenths of a joule totens of joules. In one example, the pulse width of the laser pulses canbe ten nanoseconds and the pulse energy of the laser pulses can be 50joules. In another example, the pulse width of the laser pulses can be15 nanoseconds and the pulse energy of the laser pulses can be 25joules. Higher pulse energies can be used when it is desired to inspectthicker workpieces.

Plurality of pulse stretchers 204 can include multiple pulse stretcherscoupled together in series. For instance, plurality of pulse stretchers204 can include two, three, five, ten, or more than ten pulse stretcherscoupled together in series such that an output of a first pulsestretcher is provided as an input to a second pulse stretcher, an outputof the second pulse stretcher is provided as input to a third pulsestretcher, and so forth.

Further, plurality of pulse stretchers 204 can be configured to stretchpulse widths of laser pulses output by laser 202. Plurality of pulsestretchers 204 can, for instance, be configured to stretch the pulsewidth of a laser pulse from ten nanoseconds to at least 100 nanoseconds.As described further below, one or more pulse stretchers of plurality ofpulse stretchers 204 can include two beamsplitting elements and anoptical ring cavity that are configured to split a received laser pulseinto a plurality of overlapping laser pulses with different time delays,thereby lengthening a pulse width of the received laser pulse.

In addition, one or more pulse stretchers of plurality of pulsestretchers 204 can include an optical delay controller that can beadjusted in order to alter a time delay introduced by the pulsestretcher. The time delay can be on the order of a few picoseconds, forinstance. The optical delay controller can adjust the time delay inresponse to a control signal received from feedback module 206.Adjusting the time delay can alter the shape of a laser pulse output byan individual pulse stretcher, which in turn can help to control a shapeof the overall stretched laser pulse output by plurality of pulsestretchers.

Feedback module 206 can be configured to control a shape of thestretched laser pulse output by plurality of pulse stretchers 204. Insome examples, it is useful to inspect a workpiece using a laser pulsethat has a particular shape, such as a uniform or balanced energydistribution, in order to improve the accuracy or precision of theinspection. Feedback module 206 can include one or more pulse delaycomparators 210 and a computing device 212. Each pulse delay comparatorcan be configured to compare a first laser pulse of the laser pulses toa corresponding first stretched laser pulse that has been stretched bythe plurality of pulse stretchers. Computing device 212 can beconfigured to determine, based on a result of the comparing by the pulsedelay comparator(s) 210, an adjustment to a pulse stretcher of pluralityof pulse stretchers 204, and apply the adjustment to the pulsestretcher.

Computing device 212 can include a processor and a non-transitorycomputer-readable medium storing program instructions that areexecutable by processor to carry out any of the computing devicefunctions described herein. Processor could be any type of processor,such as a microprocessor, digital signal processor, multicore processor,etc. Alternatively, computing device 212 could include a group ofprocessors that are configured to execute the program instructions, ormultiple groups of processors that are configured to execute respectiveprogram instructions.

Computing device 212 can take the form of a laptop computer, mobilecomputer, wearable computer, tablet computer, desktop computer, or othertype of computing device. As such, computing device 212 can include adisplay, an input device, and one or more communication ports throughwhich computing device 212 is configured to communicate with otherdevices of feedback module 206 as well as other devices of inspectionsystem 100 of FIG. 1.

Lens assembly 208 can be configured to direct a stretched laser pulseoutput by plurality of pulse stretchers 204 to a workpiece. As such,lens assembly can include one or more optical lenses configured to focusand/or disperse the stretched laser pulse output by plurality of pulsestretchers 204.

Detector 104, in turn, can be configured to detect a response of theworkpiece to the laser pulses. Detector 104 can take different forms,depending on the desired implementation. For instance, inspection system100 can be a laser bond inspection system, and detector 104 can be asurface motion sensor operable to detect surface motion of theworkpiece. One example of a surface motion sensor is an electromagneticacoustic transducer (EMAT). Another example of a surface motion sensoris a laser interferometer. Alternatively, inspection system 100 can bean ultrasonic inspection system, and detector 104 can be an ultrasonicsensor.

Positioning system 106 can include multiple rigid links connected bymovable joints. The joints can be moved manually by an operator.Positioning system 106 can also include a robotic positioning systemhaving a robotic manipulator and a control system configured to controlthe robotic manipulator. The robotic manipulator can include multiplerigid links connected by movable joints, and the control system cancontrol the movable joints to vary the position and/or orientation ofthe robotic manipulator. The control system can include a computingdevice, with a processor and memory storing instructions executable bythe processor to generate outputs causing the robotic manipulator tomove, for example.

End effector 108 can be an inspection head that is configured to directlaser pulses output by laser system 102 to the workpiece. End effector108 can be coupled to an end of positioning system 106. End effector 108can also include handles so that an operator can move a position of endeffector 108 relative to a workpiece. Further, end effector 108 can becoupled to a robotic manipulator of positioning system 106. In thismanner, a control system of positioning system 106 can adjust a positionof end effector 108, so as to adjust a position at which the laserpulses contact the workpiece.

FIG. 2 is a conceptual illustration 200 of laser system 102 of FIG. 1,according to an example. Conceptual illustration 200 shows laser system102 as including excimer laser 302, first pulse stretcher 304 a, secondpulse stretcher 304 b, third pulse stretcher 304 c, feedback module 306,and lens assembly 308. In addition, conceptual illustration shows aninput beamsplitter 310 and an output beamsplitter 312.

In operation, excimer laser 302 can output a first laser pulse 314.Input beamsplitter 310 can then provide a sample of first laser pulse314 to feedback module 306 before first laser pulse 314 enters firstpulse stretcher 304 a. For instance, input beamsplitter 310 can providea sample of first laser pulse 314 to a pulse delay comparator offeedback module 306.

Further, first pulse stretcher 304 a, second pulse stretcher 304 b, andthird pulse stretcher 304 can then stretch a pulse width of first laserpulse 314, yielding a first stretched laser pulse 316. Morespecifically, first pulse stretcher 304 a can stretch a pulse width offirst laser pulse 314 and output a stretched laser pulse 318. Secondpulse stretcher 304 b can then stretch a pulse width of stretched laserpulse 318 and output a stretched laser pulse 320. Still further, thirdpulse stretcher 304 c can the stretch a pulse width of stretched laserpulse 320, yielding first stretched laser pulse 316.

Output beamsplitter 312 can then provide a sample of first stretchedlaser pulse 316 to feedback module 306. For instance, outputbeamsplitter 312 can provide a sample of first stretched laser pulse 316to a pulse delay comparator of feedback module 306 for comparison withthe sample of first laser pulse 314.

FIG. 3 illustrates a pulse stretcher 300, according to an example. Pulsestretcher 300 can be one of the pulse stretchers of plurality of pulsestretchers 204 of FIG. 1. As shown in FIG. 3, pulse stretcher 300includes a first beamsplitting element 402 a, a second beamsplittingelement 402 b, an optical ring cavity 404, and an optical delaycontroller 406.

First and second beamsplitting elements 402 a, 402 b and optical ringcavity 404 are configured to split received laser pulses into aplurality of laser pulses with different time delays. In this manner,when the laser pulses overlap, a stretched laser pulse forms. Opticalring cavity 404 includes first reflective mirror 404 a, secondreflective mirror 404 b, third reflective mirror 404 c, and fourthreflective mirror 404 d. When an incident laser pulse enters pulsestretcher 400, beamsplitting element 402 a is configured to split theincident laser pulse into a first beam and a second beam. The first beamenters optical ring cavity 404, where the first beam reflects off firstreflective mirror 404 a, travels through optical delay controller 406,and is then reflected by second reflective mirror 404 b onto secondbeamsplitting element 402 b. Optical ring cavity 404 and optical delaycontroller 406 therefore introduce a time delay to the first beam.

Second beamsplitting element 402 b further splits both the second beamand the delayed first beam into two beams; one beam is directly outputand the other beam enters optical ring cavity 404 again. The beam thatenters optical ring cavity 404 reflects off third reflective mirror 404c and fourth reflective mirror 404 d and then is incident on firstbeamsplitting element 402 a to be split further.

The beamsplitting by first and second beamsplitting elements 402 a, 402b can be repeated, which causes the incident laser pulse to be splitinto a plurality of laser pulses with different time delays. During thebeamsplitting, pulse stretcher 400 can sequentially release the laserpulses of the plurality of laser pulses, so that the laser pulses form astretched laser pulse having a longer pulse width than the incidentlaser pulse. Hence, pulse stretcher 400 can output a stretched laserpulse having a longer pulse width than the incident laser pulse.

Optical delay controller 406 includes a plurality of reflective surfaces408 establishing a closed optical loop 410. Plurality of reflectivesurfaces 408 includes a one-sided mirror 412, a first mirror 414, asecond mirror 416, and a Brewster window 418. Plurality of reflectivesurfaces 408 establish a path in which an input beam can repeatedlytraverse to increase a path length that the input beam travels.

To enter closed optical loop 410, the input beam passes through anon-reflective surface of one-sided mirror 412. That is, one-sidedmirror 412 is an input interface which permits optical signals receivedby optical delay controller 406 to enter into closed optical loop 410.One-sided mirror 412 is fabricated such that input beams can passthrough the material of one-sided mirror 412 while signals received fromthe direction of Brewster window 418 are reflected towards first mirror414. Once the input beam enters closed optical loop 410 by way ofone-sided mirror 412, the input beam is reflected by first mirror 414towards second mirror 416 which in turn reflects the input beam towardsBrewster window 418. Unlike one-sided mirror 412, first mirror 414 andsecond mirror 416 are not designed to allow input beams to pass through.

Brewster window 418 can be tilted at a Brewster's angle relative to theincident direction of the optical pulse on Brewster window 418. ABrewster's angle is an angle of incidence at which light with aparticular polarization is transmitted through a transparent surfacewith no reflection. Brewster window 418 is an output interface thatpermits some of the pulse or laser beam to leave closed optical loop410. For instance, Brewster window 418 can permit a portion of the pulsein closed optical loop 410 that has achieved a desired delay to exitclosed optical loop 410. However, Brewster window 418 is only oneexample of a selective optical component that enables optical signals toexit closed optical loop 410 and is not meant to be limiting. Otheroptical components that permit optical signals to exit closed opticalloop 410 after achieving a threshold intensity or a particularpolarization can also be used.

Optical delay controller 406 can maintain a separation distance betweenat least two reflective surfaces of plurality of reflective surfaces 408to ensure optical signals exiting closed optical loop 410 have a desireddelay. To do so, optical delay controller 406 includes one or moreactuators 420 for adjusting positions of reflective surfaces ofplurality of reflective surfaces 408 relative to each other. In theexample shown in FIG. 4, actuators 420 can alter a separation distanceD1 between one-sided mirror 412 and first mirror 414 as well as aseparation distance D2 between second mirror 416 and Brewster window418. One of actuators 420 can be mechanically coupled to first mirror414 and configured to move first mirror 414 so as to increase ordecrease separation distance D1. Increasing the separation distance D1can increase the time delay introduced by optical delay controller 406.Similarly, decreasing the separation distance D1 can decrease the timedelay introduced by optical delay controller 406. Increasing ordecreasing the time delay can, in turn, change the shape of the laserpulse output by pulse stretcher 400. It can be desirable to create alaser pulse having a uniform or balanced energy distribution, to enablebetter inspection. The same or a different one of actuators 420 can bemechanically coupled to second mirror 416 to increase or decreaseseparation distance D2 in a similar manner.

Additionally or alternatively, one or more of actuators can beconfigured to increase or decrease a separation distance betweenone-sided mirror 412 and Brewster window 418 as well as increase ordecrease a separation distance between first mirror 414 and secondmirror 416 to enable more control over the path length that opticalsignals travel.

In FIG. 3, the shape of closed optical loop 410 is rectangular. In otherexamples, closed optical loop 410 may have other shapes, such as apentagonal shape or hexagonal shape.

After exiting closed optical loop 410, the delayed beam can reflect offthird mirror 422 and be directed toward second reflective mirror 404 b,so that the delay beam is inserted back into optical ring cavity 404.Hence, optical delay controller 406 can receive an input beam, add atime delay to the input beam, and output a delayed beam.

In FIG. 3, optical delay controller 406 is shown positioned betweenfirst reflective mirror 404 a and second reflective mirror 404 b. Inother examples, optical delay controller 406 can be positioned in otherpositions, such as between beamsplitting element 402 a and firstreflective mirror 404 a, between second reflective mirror 404 b andsecond beamsplitting element 402 b, between second beamsplitting element402 b and third reflective mirror 404 c, between third reflective mirror404 c and fourth reflective mirror 404 d, or between fourth reflectivemirror 404 d and first beamsplitting element 402 a. Different pulsestretchers of plurality of pulse stretchers 204 could have optical delaycontrollers positioned in different respective positions, so that eachpulse stretcher alters the shape of a received laser pulse in a slightlydifferent manner. This can enable more precise control over the overallshape of the stretched laser pulse output by plurality of pulsestretchers 204.

FIG. 4 illustrates components of feedback module 206 of FIG. 2,according to an example. As shown in FIG. 4, feedback module 206includes a first pulse delay comparator 502 a, second pulse delaycomparator 502 b, and computing device 504. First pulse delay comparator502 a and second pulse delay comparator 502 b can be in wired orwireless communication with computing device 504 by way of one or morewired or wireless communication links.

In line with the discussion above, first pulse delay comparator 502 acan be configured to compare a first laser pulse to a correspondingfirst stretched laser pulse. For instance, first pulse delay comparator502 a can be configured to compare a sample of first laser pulse 314 ofFIG. 2 to a sample of first stretched laser pulse 316 of FIG. 2.

Comparing two laser pulses can involve comparing leading edges of thetwo laser pulses or comparing trailing edges of the two laser pulses.For example, a comparison of a first laser pulse and a second laserpulse can provide an indication of a time difference between a positionof a leading edge of the first laser pulse and a leading edge of thesecond laser pulse. As another example, a comparison of a first laserpulse and a second laser pulse can provide an indication of a timedifference between a position of a trailing edge of the first laserpulse and a trailing edge of the second laser pulse. These timedifferences can be used by computing device 504 to determine anadjustment to a pulse stretcher. Additionally or alternatively, acomparison of a first laser pulse and a second laser pulse can providean indication of an amplitude difference between a leading edge of thefirst laser pulse and a leading edge of the second laser pulse, or anamplitude difference between a trailing edge of the first laser pulseand a trailing edge of the second laser pulse. These altitudedifferences can also be used by computing device 504 to determine anadjustment to a pulse stretcher.

Similarly, second pulse delay comparator 502 b can be configured tocompare a first laser pulse to a corresponding first stretched laserpulse. For instance, second pulse delay comparator 502 b can beconfigured to compare a sample of first laser pulse 314 of FIG. 3 to asample of first stretched laser pulse 316 of FIG. 2. Second pulse delaycomparator 502 b, however, can be configured to perform a differentcomparison than first pulse delay comparator 502 a. For instance, firstpulse delay comparator 502 a can be configured to compare a trailingedge of a first laser pulse and a trailing edge of a corresponding firststretched laser pulse, and second pulse delay comparator 502 b can beconfigured to compare a leading edge of the first laser pulse and aleading edge of the corresponding first stretched laser pulse.

Each of first pulse delay comparator 502 a and second pulse delaycomparator 502 b can include a detector configured to detect an opticalsignal, an analog-to-digital converter, and comparison hardware and/orsoftware. The detector can be an optical sensor that converts incidentlight into an electrical signal. This can enable the comparison hardwareto digitally compare two pulses. The comparison hardware and/or softwarecan include a comparator, such as transistor-transistor logic (TTL)comparator. The comparison hardware and/or software can also include agraphical programming application that facilitates visualization ofcharacteristics of an optical signal, such as LabVIEW provided byNational Instruments of Austin, Tex.

Computing device 504 can be configured to determine, based on a resultof a comparison by a pulse delay comparator, an adjustment to a pulsestretcher, and apply the adjustment to the pulse stretcher. Forinstance, computing device 504 can be configured to determine, based ona result of a comparison by first pulse delay comparator 502 a, anadjustment to a first pulse stretcher, and apply the adjustment to thefirst pulse stretcher. In addition, computing device 504 can beconfigured to determine, based on a result of a comparison by secondpulse delay comparator 502 b, an adjustment to a second pulse stretcher,and apply the adjustment to the second pulse stretcher.

A result of a comparison by a pulse delay comparator can include a timedifference. Computing device 504 could be configured to make a firstadjustment if the time difference is greater than a threshold, but tomake a second adjustment if the time difference is less than or equal tothe threshold. Similarly, a result of a comparison by a pulse delaycomparator can include an amplitude difference. Computing device 504could be configured to make a first adjustment if the amplitudedifference is greater than a threshold, but to make a second adjustmentif the amplitude difference is less than or equal to the threshold. Thefirst adjustment could be designed to decrease the amplitude different,and the second adjustment could be designed to increase the amplitudedifference.

The first adjustment and the second adjustment can include an increaseor a decrease to a time delay introduced by a pulse stretcher. Forinstance, computing device 504 can be configured to cause an actuator ofan optical delay controller of a pulse stretcher to adjust a separationdistance between at least two reflective surfaces of a plurality ofreflective surfaces of the optical delay controller. Computing device504 can cause the actuator to adjust the separation distance by sendinga control signal to the actuator or to a control system of the opticaldelay controller. Adjusting the separation distance can modify the shapeof subsequent laser pulses that are stretched by the pulse stretcher.

FIG. 5 illustrates an ultrasonic inspection system 600, according to anexample. Ultrasonic inspection system 600 represents an exampleimplementation of inspection system 100 of FIG. 1. As shown in FIG. 5,like inspection system 100 of FIG. 1, ultrasonic inspection system 600includes a laser system 602, a positioning system 606, and an endeffector 608. Further, ultrasonic inspection system 600 includes anultrasonic sensor 604.

Laser system 602 and/or ultrasonic sensor 604 can be positioned withinend effector 608. Laser system 602 and ultrasonic sensor 604 can also bein wired or wireless communication with each other by way of one or morecommunication links or in wired or wireless communication with a centralcomputing device. Laser system 602, ultrasonic sensor 604, positioningsystem 606, and end effector 608 can be components of a commonapparatus. The apparatus may be a portable apparatus.

Ultrasonic sensor 604 can be configured to detect a response of aworkpiece to a laser pulse or laser pulses provided to the workpiece bylaser system 602. For instance, ultrasonic sensor 604 can be anultrasonic transducer configured to detect ultrasonic waves.

FIG. 6 illustrates a laser bond inspection system 700, according to anexample. Laser bond inspection system 700 represents an exampleimplementation of inspection system 100 of FIG. 1. As shown in FIG. 7,like inspection system 100 of FIG. 1, laser bond inspection system 700includes a laser system 702, a positioning system 706, and an endeffector 708. Further, laser bond inspection system 700 includes asurface motion sensor 704.

Laser system 702 and/or surface motion sensor 704 can be positionedwithin end effector 708. Laser system 702 and surface motion sensor 704can also be in wired or wireless communication with each other by way ofone or more communication links or in wired or wireless communicationwith a central computing device. Laser system 702, surface motion sensor704, positioning system 706, and end effector 708 can be components of acommon apparatus. The apparatus may be a portable apparatus.

Surface motion sensor 704 can be configured to detect a response of aworkpiece to a laser pulse provided to the workpiece by laser system702. For instance, surface motion sensor 704 can be configured to detectsurface motion on a surface of the workpiece, with the surface motionbeing indicative of a failure of an adhesive bond. Surface motion sensorcan, for example, include a laser interferometer or an EMAT.

FIG. 7 shows a flowchart of a method 800, according to an example.Method 800 shown in FIG. 7 presents an embodiment of a method that, forexample, could be used with one of the systems shown in FIGS. 1, 5, and6, for example, or any of the systems disclosed herein. Any of theexample devices or systems described herein, such as components ofinspection system 100, may be used or configured to perform logicalfunctions presented in FIG. 7.

Method 800 can include one or more operations, functions, or actions asillustrated by one or more of blocks 802-812. Although these blocks areillustrated in a sequential order, these blocks may also be performed inparallel, and/or in a different order than those described herein. Also,the various blocks may be combined into fewer blocks, divided intoadditional blocks, and/or removed based upon the desired implementation.

It should be understood that for this and other processes and methodsdisclosed herein, flowcharts show functionality and operation of onepossible implementation of present embodiments. In this regard, eachblock may represent a module, a segment, or a portion of program code,which includes one or more instructions executable by a processor forimplementing specific logical functions or steps in the process. Theprogram code may be stored on any type of computer readable medium ordata storage, for example, such as a storage device including a disk orhard drive. The computer readable medium may include non-transitorycomputer readable medium or memory, for example, such as computerreadable media that stores data for short periods of time like registermemory, processor cache, and RAM. The computer readable media may alsobe any other volatile or non-volatile storage systems. The computerreadable medium may be considered a tangible computer readable storagemedium, for example.

Initially, at block 802, the method 800 includes stretching a pulsewidth of a first laser pulse using a plurality of pulse stretcherscoupled in series so as to obtain a first stretched laser pulse. Forinstance, a first pulse stretcher of the plurality of pulse stretcherscan receive a laser pulse output by a laser, and output a stretchedlaser pulse. A second pulse stretcher of the plurality of pulsestretchers can then receive and further stretch the stretched laserpulse. This process can be repeated by each additional pulse stretcherin the plurality of pulse stretchers, until a final pulse stretcher ofthe plurality of pulse stretchers outputs a stretched laser pulse. Eachpulse stretcher of the plurality of pulse stretchers can include twobeamsplitting elements and an optical ring cavity that are configured tosplit laser pulses into a plurality of laser pulses with different timedelays. Further, one or more pulse stretchers of the plurality of pulsestretchers can include an optical delay controller, such as opticaldelay controller 406 of FIG. 4.

At block 804, the method 800 includes comparing the first laser pulseand the first stretched laser pulse. Comparing the first laser pulse andthe first stretched laser pulse can involve comparing leading edges ofthe two laser pulses or comparing trailing edges of the two laser pulsesusing a pulse delay comparator. For example, a comparison of the firstlaser pulse and the first stretched laser pulse can provide anindication of a time difference between a position of a leading edge ofthe first laser pulse and a leading edge of the first stretched laserpulse. As another example, a comparison of the first laser pulse and thefirst stretched laser pulse can provide an indication of a timedifference between a position of a trailing edge of the first laserpulse and a trailing edge of the first stretched laser pulse.Additionally or alternatively, a comparison of the first laser pulse andthe first stretched laser pulse can provide an indication of anamplitude difference between a leading edge of the first laser pulse anda leading edge of the first stretched laser pulse, or an amplitudedifference between a trailing edge of the first laser pulse and atrailing edge of the first stretched laser pulse.

Comparing the first laser pulse and the first stretched laser pulse caninvolve providing a sample of the first laser pulse to a pulse delaycomparator using an input beamsplitter and providing a sample of thefirst stretched laser pulse to the pulse delay comparator using anoutput beamsplitter.

At block 806, the method 800 includes adjusting a parameter of at leastone pulse stretcher of the plurality of pulse stretchers based on aresult of the comparing of the first laser pulse and the first stretchedlaser pulse. By way of example, a computing device, such as computingdevice 506 of FIG. 5, can determine, based on the result of thecomparing, an adjustment to at least one pulse stretcher of theplurality of pulse stretchers, and apply the adjustment to the at leastone pulse stretcher. The parameter could be a time delay introduced byan optical delay controller of the at least one pulse stretcher, forinstance.

At block 808, the method 800 includes, after adjusting the parameter,stretching a pulse width of a second laser pulse using the plurality ofpulse stretchers so as to obtain a second stretched laser pulse. Forinstance, a first pulse stretcher of the plurality of pulse stretcherscan receive the second laser pulse, stretch the second laser pulse, andoutput a stretched laser pulse. A second pulse stretcher of theplurality of pulse stretchers can receive the stretched laser pulseoutput by the first pulse stretcher, further stretched the stretchedlaser pulse, and output a stretched laser pulse to the next pulsestretcher in the plurality of pulse stretcher. This process can continueuntil a final pulse stretcher of the plurality of pulse stretchersoutputs a stretched laser pulse.

At block 810, the method 800 includes delivering the second stretchedlaser pulse to the workpiece bondline. For instance, the secondstretched laser pulse can be output through a lens assembly. Deliveringthe second stretched laser pulse to the workpiece bondline can involvecausing the second stretched laser pulse to pass through a transparentoverlay provided on the workpiece.

At block 812, the method 800 includes detecting a response of theworkpiece bondline to the second stretched laser pulse. For instance, adetector, such as surface motion sensor 704 of FIG. 6, can detectsurface motion on a surface of the workpiece, with the surface motionbeing indicative of a failure of an adhesive bond at the workpiecebondline.

FIG. 8 shows an additional operation for use with the method shown inFIG. 7. Block 902 of FIG. 8 could be performed as part of block 806 ofFIG. 7. For instance, block 902 of FIG. 8 could be performed in anexample in which the at least one pulse stretcher includes an opticaldelay controller having a plurality of reflective surfaces establishinga closed optical loop.

At block 902, FIG. 8 includes causing an actuator to adjust a separationdistance between at least two of the plurality of reflective surfaces.For instance, a computing device, such as computing device 504 of FIG.4, could cause actuator 420 of FIG. 3 to adjust a separation distancebetween one-sided mirror 412 and first mirror 414 of FIG. 3.Alternatively, computing device 504 could cause actuator 420 of FIG. 3to adjust a separation distance between second mirror 416 and Brewsterwindow 418 of FIG. 3.

FIG. 9 shows a flowchart of another method 1000, according to anexample. Method 1000 shown in FIG. 9 presents an example of a methodthat, for example, could be used with one of the systems shown in FIGS.1, 5, and 6, for example, or any of the systems disclosed herein. Any ofthe example devices or systems described herein, such as components ofinspection system 100 of FIG. 1, may be used or configured to performlogical functions presented in FIG. 9. Method 1000 may include one ormore operations, functions, or actions as illustrated by one or more ofblocks 1002-1008. Although these blocks are illustrated in a sequentialorder, these blocks may also be performed in parallel, and/or in adifferent order than those described herein. Also, the various blocksmay be combined into fewer blocks, divided into additional blocks,and/or removed based upon the desired implementation. Each block mayrepresent a module, segment, or a portion of program code, whichincludes one or more instructions executable by a processor forimplementing specific logical functions or steps in the process.

Method 1000 could be combined with one or more blocks of method 800 ofFIG. 8.

Initially, at block 1002, the method 1000 includes determining anintegrity of a workpiece bondline. Determining the integrity of theworkpiece bondline can involve determining an amount of surface motionon a surface of the workpiece using a surface motion sensor. At block1004, the method 1000 includes determining whether or not the integrityof the workpiece bondline is acceptable. For instance, determiningwhether or not the integrity of the workpiece bondline is acceptable caninvolve determining whether or not an amount of surface motion exceeds athreshold. If the amount of surface motion exceeds the threshold, theintegrity of the workpiece bondline can be deemed not acceptable.Whereas, if the amount of surface motion does not exceed the threshold,the integrity of the workpiece bondline can be deemed acceptable.

If the workpiece bondline is acceptable, then, at block 1006, anacceptance indication may be provided. For instance, an inspectionsystem may cause an audio element (e.g., a speaker or a buzzer) toprovide an audible acceptance indication and/or cause a lighting element(e.g., a light-emitting diode or a display) to provide a visualacceptance indication. Whereas, if the integrity of the workpiecebondline is not acceptable, then, at block 1008, a rejection indicationmay be provided. Like the acceptance indication, the rejectionindication may be an audible indication or a visual indication.

The providing of the acceptance indication may be optional. Forinstance, a control system may be configured to not provide anyindication if the integrity of the workpiece bondline is acceptable, butto provide a rejection indication if the integrity of the workpiecebondline is not acceptable.

The description of the different advantageous arrangements has beenpresented for purposes of illustration and description, and is notintended to be exhaustive or limited to the examples in the formdisclosed. After reviewing and understanding the foregoing disclosure,many modifications and variations will be apparent to those of ordinaryskill in the art. Further, different examples may provide differentadvantages as compared to other examples. The example or examplesselected are chosen and described in order to best explain theprinciples, the practical application, and to enable others of ordinaryskill in the art to understand the disclosure for various examples withvarious modifications as are suited to the particular use contemplated.

What is claimed is:
 1. A laser system comprising: a laser configured toprovide laser pulses; a plurality of pulse stretchers coupled togetherin series, the plurality of pulse stretchers configured to stretch pulsewidths of the laser pulses and output stretched laser pulses; a feedbackmodule comprising: a pulse delay comparator configured to compare afirst laser pulse of the laser pulses to a corresponding first stretchedlaser pulse of the stretched laser pulses, and a computing deviceconfigured to (i) determine, based on a result of the comparing by thepulse delay comparator, an adjustment to a pulse stretcher of theplurality of pulse stretchers and (ii) apply the adjustment to the pulsestretcher so as to modify a shape of a second stretched laser pulse ofthe stretched laser pulses; and a lens assembly configured to output thesecond stretched laser pulse.
 2. The laser system of claim 1, whereinthe adjustment comprises an adjustment to a time delay introduced by thepulse stretcher.
 3. The laser system of claim 2, wherein the pulsestretcher comprises an optical delay controller having a plurality ofreflective surfaces establishing a closed optical loop, and whereinapplying the adjustment to the pulse stretcher comprises causing anactuator to adjust a separation distance between at least two of theplurality of reflective surfaces.
 4. The laser system of claim 1,wherein the pulse delay comparator is configured to compare a leadingedge of the first laser pulse and a leading edge of the first stretchedlaser pulse.
 5. The laser system of claim 1, wherein the pulse delaycomparator is configured to compare a trailing edge of the first laserpulse and a trailing edge of the first stretched laser pulse.
 6. Thelaser system of claim 5, wherein the feedback module further comprisesan additional pulse delay comparator that is configured to compare aleading edge of the first laser pulse and a leading edge of the firststretched laser pulse, wherein the computing device is furtherconfigured to: (i) determine, based on a result of the comparing by theadditional pulse delay comparator, an adjustment to an additional pulsestretcher of the plurality of pulse stretchers and (ii) apply theadjustment to the additional pulse stretcher so as to further modify theshape of the second stretched laser pulse.
 7. The laser system of claim1, wherein the laser comprises an excimer laser.
 8. The laser system ofclaim 1, wherein the plurality of pulse stretchers is configured tostretch the pulse widths of the laser pulses to at least 100nanoseconds.
 9. The laser system of claim 1, wherein the pulse stretchercomprises two beamsplitting elements and an optical ring cavity that areconfigured to split the laser pulses into a plurality of laser pulseswith different time delays.
 10. The laser system of claim 1, furthercomprising: an input beamsplitter configured to provide a sample of thefirst laser pulse to the pulse delay comparator before the first laserpulse enters the plurality of pulse stretchers; and an outputbeamsplitter configured to provide a sample of the first stretched laserpulse to the pulse delay comparator.
 11. An inspection systemcomprising: a laser system comprising: a laser configured to providelaser pulses, a plurality of pulse stretchers coupled together inseries, the plurality of pulse stretchers configured to stretch pulsewidths of the laser pulses and output stretched laser pulses, a feedbackmodule configured to adjust a parameter of at least one pulse stretcherof the plurality of pulse stretchers based on a comparison of a firstlaser pulse of the laser pulses and a corresponding first stretchedlaser pulse of the stretched laser pulses, and a lens assemblyconfigured to direct a second stretched laser pulse of the stretchedlaser pulses to a workpiece after the feedback module adjusts theparameter of the at least one pulse stretcher; and a detector configuredto detect a response of the workpiece to the second stretched laserpulse.
 12. The inspection system of claim 11, further comprising: an endeffector configured to direct the second stretched laser pulse to theworkpiece; and a positioning system configured to adjust a position ofthe end effector.
 13. The inspection system of claim 11, wherein theparameter comprises a time delay introduced by the at least one pulsestretcher.
 14. The inspection system of claim 13, wherein the at leastone pulse stretcher comprises an optical delay controller having aplurality of reflective surfaces establishing a closed optical loop, andwherein adjusting the parameter of the at least one pulse stretchercomprises causing an actuator to adjust a separation distance between atleast two of the plurality of reflective surfaces.
 15. The inspectionsystem of claim 11, wherein the detector comprises an ultrasonic sensor.16. The inspection system of claim 11, wherein the detector comprises asurface motion sensor operable to detect surface motion of theworkpiece.
 17. The inspection system of claim 11, wherein the pluralityof pulse stretchers is configured to stretch the pulse widths of thelaser pulses to at least 100 nanoseconds.
 18. A method for inspecting aworkpiece bondline comprising: stretching a pulse width of a first laserpulse using a plurality of pulse stretchers coupled in series so as toobtain a first stretched laser pulse; comparing the first laser pulseand the first stretched laser pulse; adjusting a parameter of at leastone pulse stretcher of the plurality of pulse stretchers based on aresult of the comparing of the first laser pulse and the first stretchedlaser pulse; after adjusting the parameter, stretching a pulse width ofa second laser pulse using the plurality of pulse stretchers so as toobtain a second stretched laser pulse; delivering the second stretchedlaser pulse to the workpiece bondline; and detecting a response of theworkpiece bondline to the second stretched laser pulse.
 19. The methodof claim 18, wherein the at least one pulse stretcher comprises anoptical delay controller having a plurality of reflective surfacesestablishing a closed optical loop, and wherein adjusting the parametercomprises causing an actuator to adjust a separation distance between atleast two of the plurality of reflective surfaces.
 20. The method ofclaim 18, further comprising: determining, based on the response, anintegrity of the workpiece bondline; and providing an indication of theintegrity of the workpiece bondline.